To a mixture of 8.2 mg of 4-oxo-1-propyl-4,5-dihydro[1,2,4]triazolo[4,3-a]quinoxaline-7-carboxylic acid, 1.6 mg of 3-chloroaniline, 4.1 mg of 1-hydroxybenzotriazole, 8.4 μl of triethylamine, and 1 mL of N,N-dimethylformamide was added 100 mg of PS-Carbodiimide (Biotage AB), followed by stirring at 60° C. overnight. To the reaction mixture were added 50 mg of MP-Carbonate (Biotage AB) and 50 mg of PS-Isocyanate (Biotage AB) at room temperature, followed by stirring for 4 hours. The reaction mixture was filtered and the filtrate was concentrated under reduced pressure. The obtained residue was purified by preparative HPLC (methanol/0.1% aqueous formic acid solution) to obtain 0.87 mg of N-(3-chlorophenyl)-4-oxo-1-propyl-4,5-dihydro[1,2,4]triazolo[4,3-a]quinoxaline-7-carboxamide.
